Iron ion is one of the most common and important metal ions in nature, and its valences are bivalent and trivalent. Simultaneously analyzing the two valences is important not only for biochemistry and environmental chemistry, but also in many scientific and industrial fields. For biogeochemical cycles which determine the environmental availability of trace elements at the sediment/water interface, pushes towards the development of analytical methods which might be sensitive, of practical use and able to give information on iron speciation, in particular with respect to its oxidation state. So far, atomic absorption spectroscopy (AAS), Ion chromatography (IC), inductively coupled plasma (ICP)-Atomic Emission Spectrometry (AES) and/or mass spectrometry have been generally known as analytical techniques for metal ions; however, these methods can not distinguish any difference in the metal valences. For example, the principle of AAS is to use the absorption of light to measure the concentration of gas-phase atoms which depend on the properties of metal, not ion. IC is also a very common method, but its principle is: Ions in solution of a certain concentration can conduct electrical charges, with a linear correlation between the concentration of the ions and the current conducted. Also this method needs pretreatment and special chelating reagent when used for different ions determination. For those methods, the process becomes very complex and expensive when they are used for determination of Fe (II)/Fe (III) concentration in the same solution. The common procedures for those methods are: first, Fe (II) is complexed with specific chelating agents, and then measured by this method. Fe (III) is subsequently reduced to Fe (II) and the total iron is determined, and then yielding the concentration of Fe (III). Those methods need to measure the sample twice and the instrument is expensive. Other methods such as: Solid Phase Colorimetry based on Tristimulus Chromaticity Diagram (SPC-TCD), Potentiometry and ion-exchange voltammetry (PIEV), differential-pulse cathodic stripping voltammetry (DPCSV), and Cyclic and Multiple Square-Wave Voltammetry (CMSWV) are not as expensive as AAS or IC, but they can only be used for total iron ion determination (only one of the species) and most of them are limited by tedious procedure.
Accordingly, a need exists for new methods for measuring multivalent cations in solution simultaneously. A further need exists for a system that employs that method.